There are many sensors on the market today. These sensors are designed to convert a physical phenomenon into an electrical signal. For example,
Barometric Pressure Sensor                Measures atmospheric pressure                    Altitude            Weather                        
Accelerometer                Measures direction of gravity                    Linear movement            Tilt (Roll, Pitch)            Shock sensing            Free-fall                        
Gyroscope                Measures Coriolis effect                    Heading Changes            Rotation                        
Magnetic Field Sensor                Measures direction of magnetic field                    Compass            Absolute Heading                        
Accelerometers are the most widely used MEMS sensors with millions integrated into cars by the automotive industry. As said above, the linear accelerometers can sense the linear motion and can provide a measure of tilt. With a 3D accelerometer, motion in (x, y, z) can be sensed. In addition, the direction of the gravity can be used to estimate the roll (θ) and pitch (φ) (see FIG. 1).